In general, NTSC/PAL color television systems transmit a composite video signal obtained by multiplexing a luminance signal (Y) and a chrominance signal (C) quadrature-amplitude-modulated to a subcarrier frequency. A receiver should separate the luminance signal Y and the chrominance signal C from the composite video signal using an appropriate method in order to facilitate image display and signal processing.
FIG. 1 represents a composite video signal (CVBS, Composite Video with Blanking and Synchronization signal) and luminance and chrominance signals Y and C separated from the composite video signal CVBS. Referring to FIG. 1, a high-frequency chrominance signal C remains in a portion A of the separated luminance signal Y.
FIG. 2 is a diagram for explaining an example of separating Y/C from a composite video signal CVBS of a still video. Referring to FIG. 2, the composite video signal CVBS of the Nth frame of the still video corresponds to the sum of the luminance signal Y and the chrominance signal C. The composite video signal CVBS of the (N+1)th frame corresponds to a signal obtained by subtracting the chrominance signal C from the luminance signal Y. That is, the luminance signal Y of the composite video signal CVBS of the (N+1)th frame has the same phase as that of the luminance signal of the composite video signal CVBS of the Nth frame but the chrominance signal C has a phase opposite to that of the chrominance signal C of the composite video signal CVBS of the Nth frame. It may be relatively simple to separate the luminance signal Y and the chrominance signal C from the composite video signal CVBS of the still video using a complementary Y/C separation method.
FIG. 3 is a diagram for explaining an example of separating Y/C from a composite video signal CVBS of a moving image. Referring to FIG. 3, the composite video signal CVBS of the (N+1)th frame of the moving image is delayed from the composite video signal CVBS of the Nth frame by T/2. Accordingly, the luminance signal Y and the chrominance signal C of the composite video signal CVBS of the (N+1)th frame have phases opposite to the phases of the luminance signal Y and the chrominance signal C of the composite video signal CVBS of the Nth frame. In this case, it may not be as simple to separate the luminance signal Y and the chrominance signal C from the composite video signal CVBS of the moving image using the complementary Y/C separation method.
FIG. 4 is a diagram for explaining another example of separating Y/C from a composite video signal CVBS of a moving image having relatively high levels of motion. Referring to FIG. 4, it may be difficult to separate Y/C from the composite video signal CVBS of the moving image with this level of motion only using the Nth frame and the (N+1)th frame. In this case, Y/C separation can be performed using the (N+2)th frame in addition to the Nth and (N+1)th frames, which may be more complicated than the other approaches described above.
Some conventional Y/C separation techniques use a spatial filter and a spatio-temporal filter. The spatial filter can be simpler and cheaper than the spatio-temporal filter. The spatio-temporal filter can improve the performance of the spatial filter because it uses correlation on the time axis of a video signal. Recently, a spatio-temporal Y/C separation filter has been popularized because of demands for images with high picture quality.
However, according to FIG. 5, when an RF component of the luminance signal Y and an RF component of the chrominance signal C are disposed in the same spectrum band, it may be difficult to separate the luminance signal Y and the chrominance signal C even when a high-performance spatio-temporal Y/C separation filter is used.
When Y/C separation is not properly performed, cross-luma and cross-color artifacts may occur. The cross-luma occurs when a C component exists in the separated luminance signal Y resulting in dotted artifacts. The cross-luma artifact may not be obvious due to characteristics of display devices and the human eye. The cross-color occurs when a Y component exists in the separated chrominance signal C resulting in a rainbow pattern artifact. When the cross-color artifact is generated, colors are changed for every frame to be unpleasant to the eye.